A rotogravure printing press uses a direct printing process where the ink is transferred directly to a printing surface (e.g. a paper or plastic web) from small cells that are engraved into the surface of a gravure cylinder. The rotogravure printing press typically consists of the gravure cylinder, a doctor blade, an impression roller, and an ink pan system. In operation, the gravure cylinder is rotated in the filled ink pan system and the engraved cells pickup the ink as the gravure cylinder turns. Excess ink is wiped from the gravure cylinder surface by the doctor blade and is returned to the ink pan system. The printing surface (e.g. the paper or plastic web) is pressed onto the gravure cylinder surface by the impression roller, resulting in a direct ink transfer from the inked cells of the gravure cylinder to the printing surface.
The typical ink pan system consists of two pans, an inner pan and an outer pan. Each pan may have a concave shape. The inner pan holds the ink for pickup by the rotating gravure cylinder. The outer pan receives ink from the inner pan via gravity. In operation, the ink is pumped into the inner pan and then drains through small holes in the bottom of the inner pan and/or cascades over the inner pan into the outer pan. The ink drains out of the bottom of the outer pan through an opening into a drain hose and then into an ink sump via gravity.
There are several problems with the foregoing two pan system. Some of the problems include: the amount of ink needed to operate the rotogravure press, the amount of ink left in the ink pan system after operation, the pump pressure needed to sustain the amount of ink in the ink pan system, the amount of man hours needed to clean parts after operation, and the scumming, bubbling, and swirling affect of the ink in front of the gravure cylinder which causes color voids in the print.
U.S. Pat. No. 7,243,600 discloses a single pan system for a rotogravure printing press designed to overcome some of the problems of the two pan system. This single ink pan design has a reservoir and a dam located within the reservoir that divides the reservoir into an intake section and an outtake section. A gate is provided within the dam that, when opened, allows ink in the intake section to be emptied into the outtake section. While the gate is closed, the dam maintains the ink in the intake section up to the height of the dam and any excess ink flows over the dam into the outtake section. This process of removing the excess, or top layer of ink, helps reduce the amount of scumming, bubbling, and the swirling effect that take place in front of the gravure cylinder. In addition, because of the single pan design, less ink is required to run the rotogravure printing press than a two pan system.
Although this single pan design reduces the amount of ink required to operate and helps reduce the amount of scumming, bubbling, and the swirling effect that take place in front of the gravure cylinder, there are several other problems with this single pan system. First, during the printing process ink may splash out of the pan or into the bearings of the gravure cylinder journal. These ink splashes result in wasted ink and require the bearings of the gravure cylinder journal to be replaced frequently. Second, the single ink pan design requires unnecessary pump pressure to pump the ink over the walls of the reservoir into and out of the pan. Third, the gate provided in the dam requires an operator to reach into the pan and manually pull and hold the gate into the open position, which may result in pollution and waste of the ink in the pan. Fourth, the previous design of the gate allowed the gate to be removed from the dam when an operator was merely trying to open the gate. This forces an operator to try and find and fit the gate back into its slot, which adds to the down time of the printing press. Fifth, the vortex promoter at the bottom of the intake section traps ink, or any other liquids (i.e., cleaning fluids), above the vortex promoter in the intake section, thus not allowing the intake section to be completely cleaned. And sixth, the doctor blade setup used on the single pan design required the doctor blade to be replaced frequently, which is an added cost due to the downtime required of the printing press to replace the doctor blade, and the actual costs of the doctor blades themselves.
As a result of the above described problems of the single pan system for a rotogravure printing press, there is clearly a need to improve this single pan design, while still maintaining its advantages over the two pan design, i.e., less ink required and reducing the amount of scumming, bubbling, and the swirling effect that take place in front of the gravure cylinder. Accordingly, there is a need for a single pan system for a rotogravure printing press that: prevents or reduces the possibility for ink to splash from the pan system; seals the bearings of the gravure cylinder journal; provides an intake and an outtake into and out of the pan system that does not require ink to be pumped over the walls of the pan; provides a means for operating the dam gate from the exterior of the pan that allows the gate to be locked in the open position; provides a dam and gate configuration that does not allow the gate to be removed from the dam; provides a modification to the vortex promoter that allows all of the liquid from the intake section to be drained; and makes the doctor blade more efficient and last longer.
The instant invention is designed to provide an ink pan system for a rotogravure printing press that addresses all the problems mentioned above.